1. Field of the Invention
The present invention relates to a projection system, an image processing device, and a projection method. More specifically, the present invention relates to a projection system for projecting an image on a projection body by a plurality of projection units, an image processing device constituting the projection system, and a projection method executed by the projection system.
2. Description of the Related Art
Conventionally, the multi-projection technology is garnering attention, in which projected images from a plurality of projectors are arranged with areas overlapping with each other, and a single high-resolution image is projected on a screen.
A known example of the above multi-projection technology is described in Japanese Patent No. 3908255 (Patent Document 1). In the image projection system of Patent Document 1, a reference image is projected onto a screen from the respective projectors. The reference image includes four or more feature points whose coordinate positions are known in advance. The reference image is a known image such as a grating pattern in which bright spots or crosses are arranged with fixed intervals. Then, the positions of the feature points in the reference image, which is taken by (imaged by) a digital camera, are detected. Based on the detected positions of four or more feature points of each projector, the projection image of each projector is deformed, and the overlapping areas are detected and a blending process is performed. The projected images which have been deformed and which have undergone the blending process, are projected from the plurality of projectors, and arranged on the screen with areas overlapping each other, to form a single high-resolution image.
When performing the multi-projection described above, in order to align the projection images and match the scale of the projection images, it is necessary to sequentially or simultaneously project reference images from the projectors, and take images of the reference images. However, by the method of the conventional technology in which the reference images are sequentially projected from the projectors, and the images are taken a plurality of times, the camera needs to be fixed on a tripod, and the image needs to be taken such that the projection ranges of all projectors are included in the angular field. Therefore, this technology has been unsatisfactory in that equipment such as a tripod is necessary, which reduces the convenience. Furthermore, if the number of projectors increases, there have been cases where it is difficult to take an image to include the projection ranges of all projectors in the angular field at once. For example, when multi-projection is performed on the wall of a hallway, due to restrictions such as the width of the hallway, it is difficult to secure a sufficient distance for taking an image by including the projection ranges of all projectors in the angular field.
Meanwhile, by a method of the conventional technology of simultaneously projecting reference images from projectors and taking an image of the reference images, the structure patterns of bright spots and crosses in the reference images from projectors that are simultaneously projected, overlap each other, and the attribution of the patterns need to be determined in image processing. In this case, when the patterns of the different projectors adhere to each other, it is difficult to separate the patterns and determine the attribution of the patterns. Therefore, the conventional technology has been unsatisfactory.
Furthermore, Japanese Patent No. 3497805 (Patent Document 2) discloses a technology of performing split imaging, by which the image is taken without including the projection ranges of all projectors in the angular field described above. However, in order to combine the images taken by split imaging described in Patent Document 2, it is necessary to accurately control the position and the orientation of the camera when performing split imaging, and an exclusive-use position control device is required for this camera control. Therefore, the conventional technology of split imaging described in Patent Document 2 has been unsatisfactory in terms of the ease in calibration and cost. Furthermore, the problem of the structure patterns overlapping each other is not addressed in Patent Document 2.
Japanese Laid-Open Patent Publication No. 2012-47849 (Patent Document 3) is known as a technology of stack projection, in which when a plurality of projectors project images on a projection body to overlap each other, the structure patterns are simultaneously projected in an overlapping manner, an image is taken of the structure patterns, and the structure patterns are later separated. The conventional technology of Patent Document 3 discloses a method in which patterns whose wavelength regions of R, G, B have been changed for each projector are projected, and patterns whose polarization properties have been changed are projected, and the superposed patterns are separated later based on the wavelengths and the polarization properties. However, by the method of projecting patterns whose wavelength regions have been changed, the wavelength regions of R, G, B, of a projector and the wavelength regions of R, G, B, of a camera usually do not match, and therefore it has not been easy to separate the patterns into separate color signals by using a typical camera. By the method of projecting patterns whose polarization properties have been changed, an exclusive-use imaging device is necessary, which leads to increased cost.
Furthermore, Japanese Laid-Open Patent Publication No. 2011-182076 (Patent Document 4) discloses a method of simultaneously projecting, with a plurality of projectors, a plurality of types of patterns whose phases are shifted from each other, by devising a way to position the patterns so as not to overlap each other, and taking an image of the projected patterns. However, in order to ensure precision in pattern extraction, it is necessary to project patterns having a sufficient size. Meanwhile, it is necessary to reduce the pattern intervals in order to increase the spatial density of patterns for the purpose of increasing the precision in alignment. Furthermore, in an ultra-short focus projector that has recently become available, images are projected from a close distance to the screen, and therefore the projected image will easily become distorted in a non-linear manner, due to factors relevant to focusing or slight setting conditions, or slight irregularities on the screen. For these reasons, there has been a limit in the method of simultaneously projecting patterns with a plurality of projectors while avoiding the overlapping of the patterns, and taking an image of the projected patterns.
Patent Document 1: Japanese Patent No. 3908255
Patent Document 2: Japanese Patent No. 3497805
Patent Document 3: Japanese Laid-Open Patent Publication No. 2012-47849
Patent Document 4: Japanese Laid-Open Patent Publication No. 2011-182076